Net Income Per Share Attributable to Lear (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to Lear	$ 182.8	$ 331.4	$ 411.7	$ 685.1
Redeemable noncontrolling interest adjustment	(0.9)	(9.2)	5.8	(14.6)
Net income available to Lear common stockholders	$ 181.9	$ 322.2	$ 417.5	$ 670.5
Average common shares outstanding (in shares)	62,191,022	66,320,362	62,501,419	66,701,228
Dilutive effect of common stock equivalents (in shares)	163,312	387,678	233,075	431,658
Average diluted shares outstanding (in shares)	62,354,334	66,708,040	62,734,494	67,132,886
Basic net income per share available to Lear common stockholders (in dollars per share)	$ 2.92	$ 4.86	$ 6.68	$ 10.05
Diluted net income per share available to Lear common stockholders (in dollars per share)	$ 2.92	$ 4.83	$ 6.66	$ 9.99